In electron microscopes, especially transmission electron microscopes, wherein a good vacuum is required in the region of the specimen which is to be microscoped, the problem occurs that substances, which outgas from the specimen, deteriorate the vacuum, that is, the vacuum becomes contaminated. In order to avoid such a contamination of the vacuum, so-called anti-contaminators can be mounted in the region of the specimen within the vacuum column with these anti-contaminators being cooled. Gases escaping from the specimen condense on the anti-contaminators because of the lower temperature of the anti-contaminators relative to the ambient temperature within the vacuum column whereby the quality of the vacuum is retained. The anti-contaminators operate to a certain extent as cryopumps. By maintaining the quality of the vacuum in the region of the specimen, a contamination of the specimen by residual gas molecules of the vacuum, which condense on the specimen, is simultaneously reduced whereby the specimen quality is maintained over a longer time.
Furthermore, it is also possible to provide coolable specimen manipulators via which the specimen can be cooled during the electron microscopic investigation. Cooled specimen manipulators operate likewise as anti-contaminators. Furthermore, the specimen can, in this way be held at a correspondingly low temperature during the electron microscopic investigation.
For cooling the anti-contaminators and/or the specimen holder, a cooler can be provided which is arranged outside of the vacuum system. The heat of the anti-contaminator and/or of the specimen holder is conducted to this cooler. Up to now, thermal conductors of copper or copper wires have been used for conducting heat away from the anti-contaminators and/or the specimen holder to the cooler. Copper has a high linear coefficient of expansion and therefore considerable shrinkages of the thermal conductor occur when there is a cooling to the temperature of the cooler, which, as a rule, is liquid nitrogen. These changes of length must be compensated by suitable elastic supports of the cooling rod and of the vessel filled with the cryogen. This is always accompanied with cooling losses which reduce the efficiency of the cooling. Furthermore, the thermal conductivity of the copper defines a resistance for the heat flow from the anti-contaminator and/or the specimen holder to the cooler. This resistance limits the minimum temperature which can be realized at the anti-contaminator and therefore the capacity thereof.
The following publications are noted as covering the state of the art in connection with the present invention and include: U.S. Pat. Nos. 4,179,605 and 4,833,330 as well as U.S. Pat. Nos. 4,591,722 and 6,469,381. U.S. Pat. No. 6,469,381 is not in the area of particle beam apparatus but is instead directed to the area of semiconductor component elements.